The present invention relates to a device for separating a mixture of fluids, which mixture comprises gas, a lighter liquid and a heavier liquid, into the three phases, gas, lighter liquid and heavier liquid. Such a mixture of fluids is for example a mixture of gas, hydrocarbon oil and water that is produced from a subsurface reservoir.
Russian patent publication No. 2 077 364 discloses a device for separating a mixture of fluids into three phases, gas, lighter liquid and heavier liquid, having a feed inlet, a gas outlet, an outlet for the lighter liquid and an outlet for the heavier liquid, which device comprises:
an upwardly inclined Supply pipe with the feed inlet at its upstream end;
a downwardly inclined pipe having an inlet at its upper end that is connected to the outlet of the supply pipe and having a closed lower end;
a gas discharge system having an inlet that is located in the gas-filled space and an outlet that is in fluid communication with the gas outlet of the device;
a discharge system for lighter liquid having an inlet that is located in the lighter liquid-filled space and an outlet that is in fluid communication with the outlet for lighter liquid of the device; and
a discharge system for heavier liquid having an inlet arranged at the lower end of the downwardly inclined pipe and an outlet that is in fluid communication with the outlet for heavier liquid of the device.
During normal operation, a mixture of gas, lighter liquid and heavier liquid is supplied to the feed inlet of the separation device. The mixture passes upwards through the upwardly inclined supply pipe towards the inlet of the downwardly inclined pipe. In the upper end of the downwardly inclined pipe, gas is separated from the liquids that fall downwards towards the lower end of the downwardly inclined pipe. Gas, lighter liquid and heavier liquid are separately removed from the device via the respective outlets.
A disadvantage of the known separation device is that turbulence is generated in the upwardly inclined feed pipe and that counter current flow prevails in the downwardly inclined pipe, which phenomena adversely affect the separation efficiency of the device.
It is an object of the present invention to provide a device for separating a fluid mixture that has an improved separation efficiency, which separation device is specifically intended for fluid mixtures which have been transported in an upstream pipeline under such conditions that pre-separation has occurred so that the fluid mixtures arrive in the form of a stratified flow.
To this end the device for separating a mixture of fluids into three phases, gas, lighter liquid and heavier liquid, having a feed inlet, a gas outlet, an outlet for the lighter liquid and an outlet for the heavier liquid, according to the present invention comprises:
a normally horizontal supply pipe with the feed inlet at its upstream end;
an inclined pipe having an inlet at its upper end that is connected to the outlet of the supply pipe and having a closed lower end;
a gas discharge system comprising a gas riser having an inlet that is located in the gas-filled space and an outlet that is in fluid communication with the gas outlet of the device;
a discharge system for lighter liquid having an inlet that is located in the lighter liquid-filled space and an outlet that is in fluid communication with the outlet for lighter liquid of the device; and
a discharge system for heavier liquid having an inlet arranged below the bottom level of the supply pipe and an outlet that is in fluid communication with the outlet for heavier liquid of the device,
wherein the diameter of the supply pipe is selected such that during normal operation the velocities of the liquids are below a pre-determined value, wherein the ratio of the length of the supply pipe to its diameter is larger than 10 , and wherein the slope of the inclined pipe is selected such that during normal operations a stratified flow is maintained in the inclined pipe.